1. Field the Invention
The present invention relates to a valve unit and a liquid ejecting apparatus.
2. Description of the Related Art
An inkjet recording apparatus is conventionally used as a liquid ejecting apparatus that ejects liquid from a nozzle towards a target. An inkjet recording apparatus includes a carriage and a recording head that is mounted on the carriage. Printing is performed on a recording medium by discharging ink from nozzles formed in the recording head while moving the carriage with respect to the recording medium as a target.
Most kinds of inkjet recording apparatus, which are mainly utilized for home use, employ an “on-carriage type” configuration in which a plurality of ink cartridges for supplying ink to the recording head are detachably mounted on the aforementioned carriage. However, the capacity of ink cartridges in the on-carriage type of inkjet recording apparatus is limited, and when attempting to carry out a comparatively large amount of printing it is necessary to frequently replace the ink cartridges, involving time and trouble for the user.
To overcome this problem, an “off-carriage type” configuration is sometimes employed in which large-capacity ink cartridges are disposed on the case side of the inkjet recording apparatus. More specifically, the off-carriage type inkjet recording apparatus supplies ink from each of the large-capacity ink cartridges via flexible tubes to a recording head mounted on a carriage.
However, in the off-carriage type configuration, due to the routing of the tube, large pressure variations may arise in the tube running from the ink cartridges to the carriage. This decreases the efficiency of the discharge of ink from the recording head.
An inkjet recording apparatus that can solve the aforementioned problems is disclosed in, for example, International Publication No. WO 03/041964. More specifically, in the inkjet recording apparatus disclosed in that publication, ink from ink cartridges disposed in the case is received by a valve unit having a self-sealing function that is mounted on a carriage. This valve unit is equipped with an ink introducing chamber and pressure chamber, and ink supplied from the ink cartridge is fed from the ink introducing chamber to a recording head through the pressure chamber. A valve is provided between the ink introducing chamber and pressure chamber, and the opening and closing of this valve respectively enables and disenables communication between the ink introducing chamber and pressure chamber.
Accompanying a decrease in the amount of ink inside the pressure chamber, a film member compartmentalizing one part of the pressure chamber is displaced, and that displacement is directly transferred to the valve to actuate the valve.
When ink is consumed at the recording head the ink amount in the pressure chamber decreases to lower the pressure in the pressure chamber, whereby the valve enters an open state and ink is supplied from the ink introducing chamber to the pressure chamber. Thus, ink is supplied to the pressure chamber in accordance with the amount of ink consumed at the recording head, and the effect of pressure changes in the tube disposed on the upstream side of the valve unit are not transmitted to the recording head.
The inkjet recording apparatus disclosed in the aforementioned publication pressurizes ink in the ink cartridges with air to supply ink in a pressurized state to the valve unit via a tube. However, in the above publication, since the valve has a plate part that receives pressure from the ink supply side that is disposed in the ink introducing chamber, the pressure-receiving area of the valve is large. Accordingly, when ink is supplied in a pressurized state to the valve unit, the valve receives the effect of the supply pressure of the ink, thereby generating a hindrance to the working of the valve. This diminishes the self-sealing function of the valve unit and lowers the ink supply performance.
The configuration of a valve unit that is less subject to the influence of the supply pressure of ink is disclosed, for example, in Japanese Laid-Open Patent Publication No. 9-11488. More specifically, the valve unit disclosed in this publication includes a back pressure regulator that regulates the pressure of ink supplied to the recording head. This back pressure regulator is equipped with a diaphragm, a diaphragm piston, a lever, a valve seat and a nozzle.
When the back pressure (pressure on the side of the recording head past the diaphragm) in the recording head drops below a predetermined value, force is applied to the diaphragm piston by the diaphragm to rotate the lever, whereby the valve seat provided at the lever detaches from the nozzle. As a result, ink flows to the recording head.
In this Japanese Laid-Open Patent Publication No. 9-11488, while the supply pressure of ink is applied to a valve seat via a nozzle, the part of the valve seat to which pressure is applied is only the part that faces the nozzle, and the pressure-receiving area of that part is small. Therefore, the valve seat is less subject to the influence of the ink supply pressure, and even when supplying ink in a pressurized state, an influence on the function of the back pressure regulator is less likely to arise.
However, due to the structure of the back pressure regulator it is difficult to align the two contacting surfaces of the valve seat and the nozzle, and the sealing properties between the valve seat and the nozzle may be diminished. As a result, the function of the back pressure regulator may be diminished.